1. Field of the Invention
The present invention relates to a vehicle motion control device for controlling a vehicle motion by controlling braking force exerted on each wheel of front wheels and rear wheels of the vehicle.
2. Description of the Prior Arts
There has conventionally been a demand for controlling a motion of a vehicle so as to prevent the turning state of the vehicle from being unstable when a tire inflation pressure of a wheel of a vehicle is lowered. Further, when the tire inflation pressure is lowered, cornering force caused on the tire is generally reduced, so that there is a tendency that the turning state of the vehicle is in an understeer state when a tire inflation pressure of a front wheel is relatively lowered than a tire inflation pressure of a rear wheel. On the other hand, there is a tendency that the vehicle is in an oversteer state when a tire inflation pressure of a rear wheel is relatively lowered than a tire inflation pressure of a front wheel.
In view of this, a vehicle motion control device disclosed in a patent document 1 described below controls a steering angle of a rear wheel in the direction for eliminating the understeer state in case where a tire inflation pressure of a front wheel is relatively lowered than a tire inflation pressure of a rear wheel, as well as controls the steering angle of the rear wheel in the direction for eliminating the oversteer state in case where a tire inflation pressure of a rear wheel is relatively lowered than a tire inflation pressure of a front wheel. This device enables the vehicle to keep a stable turning state similar to the turning state obtained when the tire inflation pressure of each wheel is an appropriate value when the vehicle is in the turning state.
Patent Document 1
Japanese Unexamined Patent Application No. SHO62-59169
Generally speaking, if the tire inflation pressure of wheels at the outer side of the turning direction is lowered when the vehicle is in the turning state, the height of the center of the rotation of the wheel from the road surface is reduced due to the increase in the amount of deformation of the tire, resulting in that an excessive roll angle is liable to occur on the vehicle body according to the reduction in the tire inflation pressure of the wheel. The above-mentioned device can eliminate the understeer state or oversteer state that occurs based upon the reduction in the tire inflation pressure as mentioned above, but it does not consider to prevent the occurrence of the excessive roll angle on the vehicle body due to the reduction in the tire inflation pressure. Accordingly, it entails a problem that there is a possibility of the occurrence of the excessive roll angle on the vehicle body when the vehicle is in the turning state and the tire inflation pressure of a wheel at the outer side of the turning direction is lowered.